Nvs thresholding for efficient data management

ABSTRACT

For data management by a processor device in a computing storage environment, a threshold for an amount of Non Volatile Storage (NVS) space to be consumed by any particular logically contiguous storage space in the computing storage environment is established based on at least one of a Redundant Array of Independent Disks (RAID) type, a number of point-in-time copy source data segments in the logically contiguous storage space, and a storage classification. Establishing the threshold for the amount of NVS to be consumed based on the number of point-in-time copy source data segments in the logically contiguous storage space further includes considering resources needed to perform a Copy Source To Target (CST) operation required prior to the point-in-time copy source data segments being destaged.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of U.S. patent application Ser. No.14/074,085, filed on Nov. 7, 2013, which is a Continuation of U.S.patent application Ser. No. 13/629,814, filed on Sep. 28, 2012.

FIELD OF THE INVENTION

The present invention relates in general computing systems, and moreparticularly to, systems and methods for increased data managementefficiency in computing storage environments.

DESCRIPTION OF THE RELATED ART

In today's society, computer systems are commonplace. Computer systemsmay be found in the workplace, at home, or at school. Computer systemsmay include data storage systems, or disk storage systems, to processand store data. Contemporary computer storage systems are known todestage, and subsequently, demote storage tracks from cache to long-termstorage devices so that there is sufficient room in the cache for datato be written.

SUMMARY OF THE INVENTION

Computing storage environments featuring Cached control units maythreshold, or set limits, on an amount of Non Volatile Storage (NVS)space that ranks of storage are allowed to consume at any particulartime. This presents a single rank failure, for example, from consumingall of NVS space, and allows for multiple rank failures before all ofNVS is consumed by failed ranks.

Over the past several years, while the size of memory used in NVSstorage, such as Dynamic Random-Access Memory (DRAM) has grownexponentially, the speed of long term storage devices (e.g., storagedrives) has not kept pace. As such, if a particular rank is allowed, forexample, a percentage threshold allocation of NVS, it may not bepossible to destage all of this data to long-term storage devices duringquiesce/resume storage operations. A need exists for a data managementmechanism that takes these disparities and other characteristics intoaccount to improve overall performance.

Accordingly, and in light of the foregoing, various embodiments for datamanagement in a computing storage environment are provided. In oneembodiment, by way of example only, a method comprises destagingmodified data over a certain time period during a quiesce/resumeoperation of any particular logically contiguous storage space to anamount of Non Volatile Storage (NVS) space upon performing a code loadoperation by establishing a threshold for the amount of NVS space to beconsumed by the any particular logically contiguous storage space in thecomputing storage environment based on a Redundant Array of IndependentDisks (RAID) type, a number of point-in-time copy source data segmentsin the logically contiguous storage space, and a storage classification,where establishing the threshold for the amount of NVS to be consumedbased on the number of point-in-time copy source data segments in thelogically contiguous storage space further includes consideringresources needed to perform a Copy Source To Target (CST) operationrequired prior to the point-in-time copy source data segments beingdestaged.

Other system and computer program product embodiments are provided andsupply related advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readilyunderstood, a more particular description of the invention brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict only typical embodiments of the invention and are nottherefore to be considered to be limiting of its scope, the inventionwill be described and explained with additional specificity and detailthrough the use of the accompanying drawings, in which:

FIG. 1 is an exemplary block diagram showing a hardware structure forcache management in which aspects of the present invention may berealized;

FIG. 2 is an exemplary block diagram showing a hardware structure of adata storage system in a computer system according to the presentinvention in which aspects of the present invention may be realized;

FIG. 3 is a flow chart diagram illustrating an exemplary method forincreased efficiency in data management in a computing storageenvironment, again in which aspects of the present invention may berealized;

FIG. 4 is an additional flow chart diagram illustrating an exemplarymethod for performing various operations for data managementenhancement, again in which aspects of the present invention may beimplemented; and

FIG. 5 is an additional flow chart diagram of exemplary logic performedwhen data is destaged from the NVS in accordance with implementations ofthe invention.

DETAILED DESCRIPTION OF THE DRAWINGS

As mentioned previously, computing storage environments featuring Cachedcontrol units may threshold, or set limits, on an amount of Non VolatileStorage (NVS) space that ranks of storage are allowed to consume at anyparticular time. This presents a single rank failure, for example, fromconsuming all of NVS space, and allows for multiple rank failures beforeall of NVS is consumed by failed ranks.

Additional thresholding may be implemented as applied to so-called“Nearline” disk storage devices such that these devices may berecognized in the storage environment, and thresholded such that, forexample, a percentage of the NVS space that may be consumed by suchNearline devices, is set. Nearline devices have the characteristic thatwhen being overdriven, they slow down to cool, and can eventually stopif they become too hot.

In one computing storage environment, when so-called “Enterprise” andNearline ranks both exist, the collection of Nearline ranks may beallowed to consume about 50 percent (50%) of NVS, while the Enterpriseranks are allowed to consume one-hundred percent (100%) of NVS.

With the increase in NVS size (in one computing environment, NVS is 16GB in size), a rank can now take 4 GB (25%) of NVS space. On a Code loadoperation, a Quiesce/Resume operation needs to be performed. ToQuiesce/Resume a cluster in one computing storage environment, allmodified data needs to be destaged. 4 GB may be too much to destage onsuch a Quiesce/Resume operation, and may cause the Quiesce/Resume tofail.

Over the past several years, while the size of memory used in NVSstorage, such as Dynamic Random-Access Memory (DRAM) has grownexponentially, the speed of long term storage devices (e.g., storagedrives) has not kept pace. As such, if a particular rank is allowed, forexample, a percentage threshold allocation of NVS, it may not bepossible to destage all of this data to long-term storage devices duringquiesce/resume storage operations. A need exists for a data managementmechanism that takes these disparities and other characteristics intoaccount to improve overall performance.

The mechanisms of the illustrated embodiments incorporate newthresholding factors in addition to a percentage threshold of storageallowed to consume NVS. These new thresholding factors are based, forexample, on a Redundant Array of Independent Disks (RAID) type of rank,a number of point-in-time copy source tracks in the particular rank, andstorage classification (e.g., drive type(s) of the rank).

By introducing the additional thresholding factors, the mechanisms ofthe present invention ensure that, for example, the disparity betweendrive speed of the long term storage and the size of the NVS is takeninto account, thereby allowing the amount allocated from NVS to beadequately destaged to long term storage in a certain period of time,such as during the aforementioned Quiesce/Resume storage operations.

Turning to FIG. 1, a block diagram of one embodiment of a system 100 fordata management incorporating various aspects of the present inventionis illustrated. At least in the illustrated embodiment, system 100comprises a memory 102 coupled to a cache 104 and a processor 110 via abus 108 (e.g., a wired and/or wireless bus).

Memory 102 may be any type of memory device known in the art. Examplesof memory 102 include, but are not limited to, an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), an erasable programmable read-only memory(EPROM or Flash memory), an optical fiber, a portable compact discread-only memory (CD-ROM), an optical storage device, a magnetic storagedevice, or any suitable combination of the foregoing. In the variousembodiments of memory 102, storage tracks are capable of being stored inmemory 102. Furthermore, each of the storage tracks can be staged ordestaged from/to memory 102 from cache 104 when data is written to thestorage tracks.

Cache 104, in one embodiment, comprises a write cache partitioned intoone or more ranks 106, where each rank 106 includes one or more storagetracks. Cache 104 may be any cache known in the art.

During operation, the storage tracks in each rank 106 are destaged tomemory 102 in a foreground destaging process after the storage trackshave been written to. That is, the foreground destage process destagesstorage tracks from the rank(s) 106 to memory 102 while a host (notshown) is actively writing to various storage tracks in the ranks 106 ofcache 104. Ideally, a particular storage track is not being destagedwhen one or more hosts desire to write to the particular storage track,which is known as a destage conflict.

In various embodiments, processor 110 comprises or has access to a datamanagement module 112, which comprises computer-readable code that, whenexecuted by processor 110, causes processor 110 to perform datamanagement operations in accordance with aspects of the illustratedembodiments. In the various embodiments, processor 110 establishes athreshold for an amount of Non Volatile Storage (NVS) space to beconsumed by any particular logically contiguous storage space in thecomputing storage environment based on at least one of a Redundant Arrayof Independent Disks (RAID) type, a number of point-in-time copy sourcedata segments in the logically contiguous storage space, and a storageclassification.

In various other embodiments, processor 110 establishes an additionalthreshold for the amount of NVS space based on a predefined percentageassigned to the any particular logically contiguous storage space.

In various other embodiments, processor 110 establishes an NVS spacelimit for the any particular logically contiguous storage space as aminimum function of the threshold and the additional threshold.

In various other embodiments, processor 110 establishes an NVS spacelimit for the any particular logically contiguous storage space for afailback storage operation as a function of an Input/Output Operationsper Second (IOPS) determination for the any particular logicallycontiguous storage space, a computed drain time, and a minimum NVSstorage allocation.

In various other embodiments, processor 110 establishes an NVS spacelimit for the any particular logically contiguous storage space for afailback storage operation as a function of an Input/Output Operationsper Second (IOPS) determination for the any particular logicallycontiguous storage space, a computed drain time, a minimum NVS storageallocation, and a total number of data segments in the NVS.

FIG. 2 is a block diagram 200 illustrating an exemplary hardwarestructure of a data storage system in which aspects of the presentinvention may be implemented. Host computers 210, 220, 225, are shown,each acting as a central processing unit for performing data processingas part of a data storage system 200. The cluster hosts/nodes (physicalor virtual devices), 210, 220, and 225 may be one or more new physicaldevices or logical devices to accomplish the purposes of the presentinvention in the data storage system 200. A Network (e.g., storagefabric) connection 260 may be a fibre channel fabric, a fibre channelpoint-to-point link, a fibre channel over ethernet fabric or point topoint link, a FICON or ESCON I/O interface. The hosts, 210, 220, and 225may be local or distributed among one or more locations and may beequipped with any type of fabric (or fabric channel) (not shown in FIG.2) or network adapter 260 to the storage controller 240, such as Fibrechannel, FICON, ESCON, Ethernet, fiber optic, wireless, or coaxialadapters. Data storage system 200 is accordingly equipped with asuitable fabric (not shown in FIG. 2) or network adapter 260 tocommunicate. Data storage system 200 is depicted in FIG. 2 comprisingstorage controllers 240 and cluster hosts 210, 220, and 225. The clusterhosts 210, 220, and 225 may include cluster nodes.

To facilitate a clearer understanding of the methods described herein,storage controller 240 is shown in FIG. 2 as a single processing unit,including a microprocessor 242, system memory 243 and nonvolatilestorage (“NVS”) 216, which will be described in more detail below. It isnoted that in some embodiments, storage controller 240 is comprised ofmultiple processing units, each with their own processor complex andsystem memory, and interconnected by a dedicated network within datastorage system 200. Moreover, given the use of the storage fabricnetwork connection 260, additional architectural configurations may beemployed by using the storage fabric 260 to connect multiple storagecontrollers 240 together with one or more cluster hosts 210, 220, and225 connected to each storage controller 240.

In some embodiments, the system memory 243 of storage controller 240includes operation software 250 and stores program instructions and datawhich the processor 242 may access for executing functions and methodsteps associated with executing the steps and methods of the presentinvention. As shown in FIG. 2, system memory 243 may also include or bein communication with a cache 245, also referred to herein as a “cachememory”, for buffering “write data” and “read data”, which respectivelyrefer to write/read requests and their associated data. In oneembodiment, cache 245 is allocated in a device external to system memory243, yet remains accessible by microprocessor 242 and may serve toprovide additional security against data loss, in addition to carryingout the operations as described herein.

In some embodiments, cache 245 may be implemented with a volatile memoryand non-volatile memory and coupled to microprocessor 242 via a localbus (not shown in FIG. 2) for enhanced performance of data storagesystem 200. The NVS 216 included in data storage controller isaccessible by microprocessor 242 and serves to provide additionalsupport for operations and execution as described in other figures. TheNVS 216, may also referred to as a “persistent” cache, or “cache memory”and is implemented with nonvolatile memory that may or may not utilizeexternal power to retain data stored therein. The NVS may be stored inand with the cache 245 for any purposes suited to accomplish theobjectives of the present invention. In some embodiments, a backup powersource (not shown in FIG. 2), such as a battery, supplies NVS 216 withsufficient power to retain the data stored therein in case of power lossto data storage system 200. In certain embodiments, the capacity of NVS216 is less than or equal to the total capacity of cache 245.

The storage controller 240 may include a data management module 112. Thedata management module 112 may incorporate internal memory (not shown)in which the destaging algorithm may store unprocessed, processed, or“semi-processed” data. The data management module 112 may work inconjunction with each and every component of the storage controller 240,the hosts 210, 220, 225, and other storage controllers 240 and hosts210, 220, and 225 that may be remotely connected via the storage fabric260. Data management module 112 may be structurally one complete moduleor may be associated and/or included with other individual modules. Datamanagement module 112 may also be located in the cache 245 or othercomponents of the storage controller 240. Data management module 112,along with microprocessor 242 may implement aspects of the illustratedembodiments, such as establishing threshold factors as will be furtherdescribed.

The storage controller 240 includes a control switch 241 for controllinga protocol to control data transfer to or from the host computers 210,220, 225, a microprocessor 242 for controlling all the storagecontroller 240, a nonvolatile control memory 243 for storing amicroprogram (operation software) 250 for controlling the operation ofstorage controller 240, cache 245 for temporarily storing (buffering)data, and buffers 244 for assisting the cache 245 to read and writedata, and the data management module 112, in which information may beset. The multiple buffers 244 may be implemented to assist with themethods and steps as described herein.

Turning now to FIG. 3, a flow chart diagram, illustrating a generalizedmethod method 300 for data management, is depicted. Method 300 begins(step 302). One or more thresholds for an amount of NVS space to beconsumed by any particular logically contiguous storage space areestablished. The thresholds may be based on a RAID type, a number ofpoint-in-time-copy source data segments in the logically contiguousstorage space, and a storage classification. The method 300 then ends(step 306).

Turning now to FIG. 4, an additional flow chart diagram of exemplaryoperations in which aspects of the illustrated embodiments areincorporated, is depicted. Method 400 begins (step 402) with theinitialization of one or more storage devices in the computing storageenvironment, and a determination of the number of applicable devices(step 404).

In a subsequent step, the method 400 determines applicable RAID types ofindividual ranks, numbers of applicable point-in-time copy source tracksin one or more of the individual ranks, and drive types of the one ormore individual ranks (step 406). NVS threshold factors are then set to(1) a percentage amount based on the number of applicable storagedevices, and (2) other factors such as the aforementioned RAID type,point-in-time copy source data segments, and drive types (step 408).Various storage operations are then performed with the thresholdbenchmarks as will be further described (step 410). The method 400 thenends (step 412).

In one embodiment, the threshold factoring may be configured as follows.Individual ranks may be configured with a new threshold in addition tothe percentage basis of overall space (i.e., 25% of NVS). A “Rank NVSLimit” threshold may be defined as the minimum function of thepercentage threshold (again, i.e., 25% of NVS), and a defined “Rank NVSLimit for NVS Failback” benchmark for individual ranks.

In an additional embodiment, the Rank NVS Limit for NVS Failback may bedefined as a rank destage input/output per second (IOPS) metric,multiplied by a drain time, and multiplied by a minimum NVS allocation.

The Rank destage IOPS metric may, in one embodiment, be defined as anumber of destage IOPS a particular rank can do. This metric isdependent on the rank type and the drive types that make up a rank. Inone example, a RAID-5 Nearline rank may complete five hundred (500)IOPS. The aforementioned drain time may, in one embodiment, berepresented as the time that a failback operation takes to drain NVSduring a Quiesce/Resume operation. In one exemplary embodiment, thedrain time is set to about ten (10) minutes or 600 s. Finally, theaforementioned minimum NVS allocation may be represented as the minimumunit of NVS allocation. In one storage environment, the minimum NVSallocation is 4K (Kilobytes).

With all of the foregoing in view, consider the following example. Aparticular storage environment may have an accompanying rank NVS limitfor failback, with RAID-5 Nearline ranks, as (500 IOPS*600 s*4096K) asapproximately equal to 1.2 GB.

An additional factor that may be used to determine the aforementionedrank NVS limit for failback is an amount of point-in-time copy sourcetracks in NVS. When a point-in-time copy source track is destaged, thetrack may require a Copy Source To Target (CST) operation before thesource track can be destaged. A CST operation may consume a large amountof resources since the operation needs to stage data from the source,and then destage the data to the target.

To accommodate source point-in-time copy tracks, the aforementioned rankNVS limit for failback may be further defined as follows. The metric maybe set equal to the aforementioned rank destage IOPS*drain time*minimumNVS allocation*the total tracks in NVS, divided by the total sourcepoint-in-time copy tracks in NVS*3 +a total non-source point-in-copyracks in NVS. As one of ordinary skill in the art will appreciate,however, additional factors may be added or the aforementioned factorsmay be weighted to suit a particular application.

Turning now to FIG. 5, a flow chart diagram of exemplary fast writeoperation is depicted as method 500. Method 500 begins (step 502) withthe receipt of data from host that is directed to a target storagedevice (step 504). In step 506, the method 500 queries whether addingthe update would cause the rank NVS limit (as a function of the previousthresholds described) to be exceeded. If this is the case, then themethod 500 queues reconnect parameters needed to reconnect the hostproviding the update in the reconnect queue (step 508) and disconnectsfrom the host sending the update. The method 500 then ends (step 518).As a result, the storage controller will not accept updates that wouldcause the amount of NVS used for updates to the target storage device toexceed the previously described rank NVS limit.

Returning to step 506, if the rank NVS limit would not be exceeded bythe update, then the method 500 fast writes the data to the cache andNVS, and sets the destage flag to “on.” As a result of the update, thepercentage of NVS used and other variables used in the thresholdingpreviously described is recalculated (step 514), and an update completestatus is returned to the host (step 516). The method 500 then ends(again, step 518). As one of ordinary skill in the art will appreciate,various logic may be implemented in similar fashion as that described inFIG. 5 to implement the thresholding techniques described by theillustrated embodiments.

While at least one exemplary embodiment has been presented in theforegoing detailed description of the invention, it should beappreciated that a vast number of variations exist. It should also beappreciated that the exemplary embodiment or exemplary embodiments areonly examples, and are not intended to limit the scope, applicability,or configuration of the invention in any way. Rather, the foregoingdetailed description will provide those skilled in the art with aconvenient road map for implementing an exemplary embodiment of theinvention, it being understood that various changes may be made in thefunction and arrangement of elements described in an exemplaryembodiment without departing from the scope of the invention as setforth in the appended claims and their legal equivalents.

As will be appreciated by one of ordinary skill in the art, aspects ofthe present invention may be embodied as a system, method, or computerprogram product. Accordingly, aspects of the present invention may takethe form of an entirely hardware embodiment, an entirely softwareembodiment (including firmware, resident software, micro-code, etc.) oran embodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module,” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer-readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer-readable medium(s) may beutilized. The computer-readable medium may be a computer-readable signalmedium or a physical computer-readable storage medium. A physicalcomputer readable storage medium may be, for example, but not limitedto, an electronic, magnetic, optical, crystal, polymer, electromagnetic,infrared, or semiconductor system, apparatus, or device, or any suitablecombination of the foregoing. Examples of a physical computer-readablestorage medium include, but are not limited to, an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk,RAM, ROM, an EPROM, a Flash memory, an optical fiber, a CD-ROM, anoptical storage device, a magnetic storage device, or any suitablecombination of the foregoing. In the context of this document, acomputer-readable storage medium may be any tangible medium that cancontain, or store a program or data for use by or in connection with aninstruction execution system, apparatus, or device.

Computer code embodied on a computer-readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wired, optical fiber cable, radio frequency (RF), etc., or any suitablecombination of the foregoing. Computer code for carrying out operationsfor aspects of the present invention may be written in any staticlanguage, such as the “C” programming language or other similarprogramming language. The computer code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, or communication system, including, but notlimited to, a local area network (LAN) or a wide area network (WAN),Converged Network, or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).

Aspects of the present invention are described above with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in acomputer-readable medium that can direct a computer, other programmabledata processing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer-readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks. The computer program instructions may also beloaded onto a computer, other programmable data processing apparatus, orother devices to cause a series of operational steps to be performed onthe computer, other programmable apparatus or other devices to produce acomputer implemented process such that the instructions which execute onthe computer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the above figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

While one or more embodiments of the present invention have beenillustrated in detail, one of ordinary skill in the art will appreciatethat modifications and adaptations to those embodiments may be madewithout departing from the scope of the present invention as set forthin the following claims.

1. A method for data management by a processor device in a computingstorage environment, comprising: destaging modified data over a certaintime period during a quiesce/resume operation of any particularlogically contiguous storage space to an amount of Non Volatile Storage(NVS) space upon performing a code load operation by establishing athreshold for the amount of NVS space to be consumed by the anyparticular logically contiguous storage space in the computing storageenvironment based on a Redundant Array of Independent Disks (RAID) type,a number of point-in-time copy source data segments in the logicallycontiguous storage space, and a storage classification; whereinestablishing the threshold for the amount of NVS to be consumed based onthe number of point-in-time copy source data segments in the logicallycontiguous storage space further includes considering resources neededto perform a Copy Source To Target (CST) operation required prior to thepoint-in-time copy source data segments being destaged.
 2. The method ofclaim 1, further including establishing an additional threshold for theamount of NVS space based on a predefined percentage assigned to the anyparticular logically contiguous storage space.
 3. The method of claim 2,further including establishing an NVS space limit for the any particularlogically contiguous storage space as a minimum function of thethreshold and the additional threshold.
 4. The method of claim 3,further including establishing an NVS space limit for the any particularlogically contiguous storage space for a failback storage operation as afunction of an Input/Output Operations per Second (IOPS) determinationfor the any particular logically contiguous storage space, a computeddrain time, and a minimum NVS storage allocation.
 5. The method of claim3, further including establishing an NVS space limit for the anyparticular logically contiguous storage space for a failback storageoperation as a function of an Input/Output Operations per Second (IOPS)determination for the any particular logically contiguous storage space,a computed drain time, a minimum NVS storage allocation, and a totalnumber of data segments in the NVS.
 6. The method of claim 1, whereinthe any particular logically contiguous storage space is a storage rank,and the storage classification is a drive type in the storage rank.